The properties of a toner can be established, for example, through the selection of materials such as toner composition and amounts of surface additive materials used to formulate a functional toner. The charging characteristics of a toner are also dependent upon the carrier used in a developer composition, in particular the carrier coating. Toners typically comprise at least a binder resin, a colorant, and one or more external surface additives. The external surface additives are generally added in small amounts. Examples of external surface additives include silica, titanium dioxide, zinc stearate, etc.
For both black and color prints, a small particle size toner is known to improve the image quality of the prints. Due to the physics of small toner particles, particularly due to the large surface area inherent in smaller particles, problems such as high cohesion, poor flow, high charge to mass ratio (Q/m) and low charge to diameter ratio (Q/d) is typical. Problematically, the higher Q/m achieved with smaller particles limits developability, while the lower Q/d achieved with smaller particles increases undesirable background on prints. These issues have been addressed by the use of surface additives.
For example, small sized hydrophobic SiO2 particles can be employed to reduce toner cohesivity and improve flow. Small sized additives also work as charge control agents and may increase the developer Q/m. Toners having a triboelectric charging property within the range of about −30 microCoulombs/gram (μC/g) to about −45 μC/g may be achieved when using small sized silica particles as external additives, for example silica particles having average sizes less than 20 nanometers (nm), such as, for example, the materials known as R812 (˜7 nm), R805 (˜12 nm) and/or R972 (˜16 nm) available from Degussa Corporation. However, the developability at areas of low toner area coverage degrades over time. This has been attributed to the small sized additives being impacted into the toner surface over time.
The problems associated with small particle size toners have been addressed by using larger sized additives, i.e., additives having a size of 40 nanometers or larger such as, for example, RX50 silica, RX515H silica, and RY50 silica available from Nippon Aerosil Co. LTD., and/or SMT-5103 titania available from Tayca Corp. However, although certain problems related to developability are addressed, in these cases the toners do not exhibit the proper triboelectric charging (“tribo”) required by certain developer systems. Further, for toners employing these larger size particles, it is very difficult to move the developer charging tribo (Q/m) down without compromising the Q/d values and without also exhibiting charge through, i.e., the incumbent toner in the device becomes less negative or even wrong sign, i.e., positive, and the new (fresh) toner added may charge very negative. The most difficult task is to decrease the developer tribo without reducing the charge distribution (Q/d).
U.S. Pat. No. 6,521,297 to McDougall, Veregin, and Moffat, entitled “Marking Material and Ballistic Aerosol Marking Process for the Use Thereof” addresses, among other problems in the art, the issue of channel clogging, and describes a process for depositing marking material onto a substrate which comprises (a) providing a propellant to a head structure, the head structure having a channel therein, the channel having an exit orifice with a width no larger than about 250 microns through which the propellant can flow, the propellant flowing though the channel to form thereby a propellant stream having kinetic energy, the channel directing the propellant stream toward the substrate, and (b) controllably introducing a particulate marking material into the propellant steam in the channel wherein the kinetic energy of the propellant particle stream causes the particulate marking material to impact the substrate and where the particulate marking material comprises (a) toner particles which comprise a resin and a colorant, the particles having an average particle diameter of no more than about 7 microns and a particle geometric size distribution (GSD) equal to no more than about 1.25, the toner particles being prepared by an emulsion aggregation process, and (b) hydrophobic semiconductive metal oxide in combination with silica dioxide particles added by a dry blending process onto the toner particles. In this system, the silica controls the triboelectric charging and toner flow and the mixture of insulative and semiconductive titanium dioxide increases the overall bulk conductivity of the toner and provides excellent resistance to changes associated with relative humidity (RH). It is also known in the art that the incumbent fresh toner must have a very short time to mix with developer inside the developer housing, preferably this charge sharing should occur within about 1 to 2 minutes of mixing, more preferably between 30 to 60 seconds, and most preferably between 5 to 30 seconds.
U.S. Pat. No. 5,510,220, to Nash, Hanzlik, Muller and Hodgson, entitled “Conductive Developer Compositions With Surface Additives” describes a developer composition comprised of negatively charged toner particles comprised of crosslinked polyester resin particles, pigment particles, and a surface additive mixture comprised of metal salts of fatty acids in an amount of from about 0.2 to about 0.5 weight percent, metal oxide particles in an amount of from about 0.3 to about 1 weight percent, and silica particles in an amount of from about 0.2 to about 0.5 weight percent; and carrier particles comprised of a core with a coating thereover containing a conductive component.
U.S. Pat. No. 6,503,677 to Gutman, Grushkin, and Ruhland, entitled “Emulsion Aggregation Toner Particles Coated With Negatively Chargeable and Positively Chargeable Additives and Method of Making Same” describes an emulsion aggregation toner comprised of toner particles comprising polymer binder and colorant and a surface additive package comprising at least titania, at least one negative additive negatively chargeable to a reference carrier, and at least one positive additive positively chargeable to the reference carrier.
U.S. Pat. No. 6,087,059 to Duggan, Henderson, Stamp, Silence, Hollenbaugh, Gutman, Grushkin, and Ruhland, entitled “Toner and Developer Compositions” describes a toner comprised of resin, colorant, and a surface additive mixture comprised of two coated silicas, and a coated metal oxide, wherein the two coated silicas are comprised of a first silica and a second silica, and wherein the first coated silica contains a coating of an alkyl silane and an amino alkyl silane.
U.S. Pat. No. 6,214,507 to Sokol and Gutman entitled “Toner Compositions” describes a toner composition comprised of binder, colorant, and a surface additive of a coated silica and wherein the silica possesses a BET surface area, in m2/g, of from about 35 to about 65, a bulk density, in grams/liter, of from about 40 to about 60, and wherein the size diameter determined from the BET measurement is from about 20 to about 100 nanometers, and wherein the silica is coated with a mixture of γ-aminopropyltriethoxysilane and hexamethyldisilazane, and wherein the silica coated additive is of a size diameter of from about 25 to about 75 nanometers, and wherein the aggregate of the coated silica size diameter is about 225 to about 400 nanometers.
U.S. Pat. No. 6,379,856 to Sokol and Gutman, entitled “Toner Compositions” describes a toner comprised of binder, colorant and a surface additive mixture of a coated silica and a metal oxide, wherein the silica is coated with a mixture of γ-aminopropyltriethoxysilane and hexamethyldisilazane, wherein the metal oxide is titanium dioxide coated with decylsilane, and wherein the silica has a bulk density of from about 40 to about 60 grams/liter.
U.S. Pat. No. 6,203,960 to Ciccarelli, Bayley, and Pickering, entitled “Toner Compositions” describes a toner composition comprised of binder, colorant, and a toner particle surface additive component comprised of a first coated fumed silica surface coated with a first major amount of an alkylsilane compound present in an amount of from about 3 to about 20 weight percent based on the weight of the fumed silica and a second minor amount of an aminoalkylsilane compound present in an amount of from about 3 to about 700 parts per million of basic nitrogen (N:) based on the weight of the fumed silica.
The disclosures of the foregoing are incorporated herein by reference in their entireties.
What is still desired is a toner having a surface additive package to control toner charging, improve developability, and prevent background defects during imaging and printing, as well as improve RH sensitivity of the developer.